Methods and systems of automatically detecting an impedance of one or more electrodes in a cochlear implant system

ABSTRACT

An exemplary method includes a sound processing unit 1) directing an implantable cochlear stimulator coupled to a plurality of electrodes to generate an electrical stimulation current in accordance with one or more stimulation parameters, 2) automatically detecting an impedance of at least one of the electrodes, and 3) directing, in accordance with the detected impedance, the implantable cochlear stimulator to adjust a pulse width of the electrical stimulation current to maintain constant a total electric charge level of the electrical stimulation current.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/342,859 by Abhijit Kulkarni et al., filed onDec. 23, 2008, and entitled “METHODS AND SYSTEMS OF AUTOMATICALLYDETECTING AN IMPEDANCE OF ONE OR MORE ELECTRODES IN A COCHLEAR IMPLANTSYSTEM,” which application is incorporated herein by reference in itsentirety.

BACKGROUND INFORMATION

The sense of hearing in human beings involves the use of hair cells inthe cochlea that convert or transduce acoustic signals into auditorynerve impulses. Hearing loss, which may be due to many different causes,is generally of two types: conductive and sensorineural. Conductivehearing loss occurs when the normal mechanical pathways for sound toreach the hair cells in the cochlea are impeded. These sound pathwaysmay be impeded, for example, by damage to the auditory ossicles.Conductive hearing loss may often be helped by the use of conventionalhearing aids that amplify sound so that acoustic signals reach thecochlea and the hair cells. Some types of conductive hearing loss mayalso be treated by surgical procedures.

Sensorineural hearing loss, on the other hand, is due to the absence orthe destruction of the hair cells in the cochlea which are needed totransduce acoustic signals into auditory nerve impulses. Thus, peoplewho suffer from sensorineural hearing loss are unable to derive anybenefit from conventional hearing aid systems.

To overcome sensorineural hearing loss, numerous cochlear implantsystems—or cochlear prosthesis—have been developed. Cochlear implantsystems generally employ an array of electrodes that is inserted intothe cochlear duct. One or more electrodes of the array selectivelystimulate different auditory nerves at different places in the cochleabased on the pitch of a received sound signal. Within the cochlea, thereare two main cues that convey “pitch” (frequency) information to thepatient. These are (1) the place or location of stimulation along thelength of a cochlear duct and (2) the temporal structure of thestimulating waveform. In the cochlea, sound frequencies are mapped to a“place” in the cochlea, generally from low to high sound frequenciesmapped from the apical to basilar direction. The electrode array isfitted to the patient to arrive at a mapping scheme such that electrodesnear the base of the cochlea are stimulated with high frequency signals,while electrodes near the apex are stimulated with low frequencysignals.

Each electrode implanted within a cochlea has a certain impedanceassociated therewith. These impedance values are often used to determineone or more stimulation parameters during an initial fitting session tofit a cochlear implant system to a patient. However, electrodeimpedances may change over time, thus resulting in decreased soundquality, distorted pitch, and/or system malfunction.

SUMMARY

Methods of automatically detecting an impedance of one or moreelectrodes in a cochlear implant system include providing an implantablecochlear stimulator coupled to one or more electrodes, generating anelectrical stimulation current with the implantable cochlear stimulatorin accordance with one or more stimulation parameters, automaticallydetecting an impedance of at least one of the electrodes in accordancewith a predefined schedule, and performing a predefined action inaccordance with the detected impedance.

Systems for detecting an impedance of one or more electrodes in acochlear implant system include an implantable cochlear stimulator, oneor more electrodes electrically coupled to the implantable cochlearstimulator, and a sound processing unit. The sound processing unit isconfigured to direct the implantable cochlear stimulator to apply astimulation current to a stimulation site within a patient via at leastone of the electrodes, automatically detect an impedance of at least oneof the electrodes in accordance with a predefined schedule, and performa predefined action in accordance with the detected impedance.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of theprinciples described herein and are a part of the specification. Theillustrated embodiments are merely examples and do not limit the scopeof the disclosure.

FIG. 1 illustrates an exemplary cochlear implant system according toprinciples described herein.

FIG. 2 is a functional block diagram of an exemplary sound processingunit and implantable cochlear stimulator according to principlesdescribed herein.

FIG. 3 illustrates an exemplary stimulation current pulse that may bedelivered to neural tissue via one or more of stimulation channelsaccording to principles described herein.

FIG. 4 illustrates an exemplary electrode configuration according toprinciples described herein.

FIG. 5 illustrates an exemplary stimulation current pulse that may bedelivered to neural tissue via one or more of stimulation channelsaccording to principles described herein.

FIG. 6 illustrates an exemplary system configured to dynamically focusone or more excitation fields produced by current steering electrodes

FIG. 7 is a diagram illustrating various possible stimulation sites inthe tissue of a patient and illustrates the concept of current steeringaccording to principles described herein.

FIG. 8 is a block diagram that illustrates the main steps associatedwith a method according to principles described herein.

DETAILED DESCRIPTION

Methods and systems of automatically detecting an impedance of one ormore electrodes in a cochlear implant system are described herein. Insome examples an implantable cochlear stimulator, one or more electrodeselectrically coupled to the implantable cochlear stimulator, and a soundprocessing unit are provided. The sound processing unit may beconfigured to direct the implantable cochlear stimulator to apply astimulation current to a stimulation site within a patient via at leastone of the electrodes, automatically detect an impedance of at least oneof the electrodes in accordance with a predefined schedule, and performa predefined action in accordance with the detected impedance. In thismanner, suboptimal performance of the cochlear implant system related toa change in impedance may be diagnosed and remedied.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present systems and methods. It will be apparent,however, to one skilled in the art that the present systems and methodsmay be practiced without these specific details. Reference in thespecification to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment. Theappearance of the phrase “in one embodiment” in various places in thespecification are not necessarily all referring to the same embodiment.

To facilitate an understanding of the methods and systems describedherein, an exemplary cochlear implant system 100 will now be describedin connection with FIG. 1. Exemplary cochlear implant systems suitablefor use as described herein include, but are not limited to, thosedisclosed in U.S. Pat. Nos. 4,400,590; 4,532,930; 4,592,359; 4,947,844;5,824,022; 6,219,580; 6,272,382; and 6,308,101. All of these listedpatents are incorporated herein by reference in their respectiveentireties.

As shown in FIG. 1, the cochlear implant system 100, also referred toherein as a cochlear prosthesis, includes an external sound processorportion 110 and an implanted cochlear stimulation portion 120. The soundprocessor portion 110 may include a sound processing unit 130, amicrophone 140, and/or additional circuitry as best serves a particularapplication. The cochlear stimulation portion 120 may include animplantable cochlear stimulator (ICS) 150, a lead 160 with an array ofelectrodes 170 disposed thereon, and/or additional circuitry as bestserves a particular application. It will be recognized that the soundprocessor portion 110 may alternatively be located internal to thepatient.

The microphone 140 of FIG. 1 is configured to sense acoustic signals andconvert the sensed signals to corresponding electrical signals. Theelectrical signals are sent to the sound processing unit 130 over anelectrical or other suitable link. Alternatively, the microphone 140 maybe connected directly to, or integrated with, the sound processing unit130.

The sound processing unit 130 may include any combination of hardware,software, and/or firmware as best serves a particular application. Forexample, the sound processing unit 130 may include one or moreprocessors, digital signal processors (DSPs), filters, memory units,etc. In some examples, as will be described in more detail below, thesound processing unit 130 may include one or more alert facilities (notshown) configured to convey one or more alerts or other communicationsto a patient.

In some examples, the sound processing unit 130 may be configured toprocess the converted acoustic signals in accordance with a selectedsound processing strategy to generate appropriate control signals orstimulation parameters for controlling the ICS 150. The electricalstimulation parameters may control various parameters of the stimulationcurrent applied to a stimulation site including, but not limited to,frequency, pulse width, amplitude, waveform (e.g., square orsinusoidal), electrode polarity (i.e., anode-cathode assignment),location (i.e., which electrode pair or electrode group receives thestimulation current), burst pattern (e.g., burst on time and burst offtime), duty cycle or burst repeat interval, ramp on time, and ramp offtime of the stimulation current that is applied to the stimulation site.

It will be recognized that the sound processing unit 130 shown in FIG. 1is merely illustrative of the many different sound processing units thatmay be used in connection with the present systems and methods. Forexample, the sound processing unit 130 may include a behind-the-ear(BTE) unit configured to be positioned behind the ear. Alternatively,the sound processing unit 130 may include a portable speech processor(PSP) device, a conventional hearing aid, or any other type of soundprocessing unit. In certain examples, the sound processing unit 130 maybe removed from behind the ear or other operating location by thepatient prior to sleeping and replaced upon waking.

The lead 160 of FIG. 1 is adapted to be inserted within a duct of apatient's cochlea. As shown in FIG. 1, the lead 160 includes an array ofelectrodes 170 disposed along its length. It will be recognized that anynumber of electrodes 170 may be disposed along the lead 160 as may servea particular application.

Each of the electrodes 170 is electrically coupled to the implantablecochlear stimulator 150. Electronic circuitry within the implantablecochlear stimulator 150 may therefore be configured to apply stimulationcurrent to selected pairs or groups of electrodes 170 in accordance witha specified stimulation pattern controlled by the sound processing unit130.

As mentioned, the implantable cochlear stimulator 150 and lead 160 maybe implanted within the patient while the sound processing unit 130 andthe microphone 140 are configured to be located outside the patient,e.g., behind the ear. Hence, the implantable cochlear stimulator 150 andthe sound processing unit 130 may be transcutaneously coupled via asuitable data or communications link 180. The communications link 180allows power and control signals to be sent from the sound processingunit 130 to the implantable cochlear stimulator 150. In someembodiments, data and status signals may also be sent from theimplantable cochlear stimulator 150 to the sound processing unit 130.

The external and implantable portions of the cochlear implant system 100may each include one or more coils configured to transmit and receivepower and/or control signals via the data link 180. For example, theexternal portion 110 of the cochlear implant system 100 may include anexternal coil 190 and the implantable portion of the cochlear implantsystem 120 may include an implantable coil 195. The external coil 190and the implantable coil 195 may be inductively coupled to each other,thereby allowing data and power signals to be wirelessly transmittedbetween the external portion and the implantable portion of the cochlearimplant system 100. Because in certain embodiments, the external portion110 of the cochlear implant system 100 may not always be within closeproximity to the implantable portion of the cochlear implant system 120,such as when the external portion 110 is removed for sleeping, thesystem may be configured to recognize when the implantable coil 195 andthe external coil 190 are within range of one another.

FIG. 2 is a functional block diagram of an exemplary sound processingunit 130 and implantable cochlear stimulator 150. The functions shown inFIG. 2 are merely representative of the many different functions thatmay be performed by the sound processing unit 130 and/or the implantablecochlear stimulator 150. A more complete description of the functionalblock diagram of the sound processing unit 130 and the implantablecochlear stimulator 150 is found in U.S. Pat. No. 6,219,580, which isincorporated herein by reference in its entirety.

As shown in FIG. 2, the microphone 140 senses acoustic information, suchas speech and music, and converts the acoustic information into one ormore electrical signals. These signals are then amplified in audiofront-end (AFE) circuitry 210. The amplified audio signal is thenconverted to a digital signal by an analog-to-digital (A/D) converter220. The resulting digital signal is then subjected to automatic gaincontrol using a suitable automatic gain control (AGC) function 230.

After appropriate automatic gain control, the digital signal is thenprocessed in one of a number of digital signal processing or analysischannels 240. For example, the sound processing unit 130 may include,but is not limited to, eight analysis channels 240. Each analysischannel 240 may respond to a different frequency content of the sensedacoustical signal. In other words, each analysis channel 240 includes aband-pass filter (BP1-BPFm) 250 or other type of filter such that thedigital signal is divided into m analysis channels 240. The lowestfrequency filter may be a low-pass filter, and the highest frequencyfilter may be a high-pass filter.

As shown in FIG. 2, each of the m analysis channels 240 may also includean energy detection stage (D1-Dm) 260. Each energy detection stage 260may include any combination of circuitry configured to detect the amountof energy contained within each of the m analysis channels (240). Forexample, each energy detection stage 260 may include a rectificationcircuit followed by an integrator circuit. As will be described in moredetail below, the cochlear implant system 100 may be configured todetermine which of the m analysis channels 240 are presented to thepatient via the stimulation channels 290 by analyzing the amount ofenergy contained in each of the m analysis channels 240.

After energy detection, the signals within each of the m analysischannels 240 are forwarded to a mapping stage 270. The mapping stage 270is configured to map the signals in each of the m analysis channels 240to one or more of M stimulation channels 290. In other words, theinformation contained in the m analysis channels 240 is used to definethe stimulation current pulses that are applied to the patient by theimplantable cochlear stimulator 150 via the M stimulation channels 290.As mentioned previously, pairs or groups of individual electrodes 170make up the M stimulation channels.

In some examples, the mapped signals are serialized by a multiplexer 128and transmitted to the implantable cochlear stimulator 150. Theimplantable cochlear stimulator 150 may then apply stimulation currentvia one or more of the M stimulation channels 290 to one or morestimulation sites within the patient's cochlea. As used herein and inthe appended claims, the term “stimulation site” will be used to referto a target area or location at which the stimulation current isapplied. For example, a stimulation site may refer to a particularlocation within the neural tissue of the cochlea. Through appropriateweighting and sharing of currents between the electrodes 170,stimulation current may be applied to any stimulation site along thelength of the lead 180.

FIG. 3 illustrates an exemplary stimulation current pulse 130 that maybe delivered to neural tissue via one or more of the stimulationchannels 129. The stimulation current pulse 300 of FIG. 3 is biphasic.In other words, the pulse 300 includes two parts—a negative first phasehaving an area A1 and a positive second phase having an area A2. In someimplementations, the negative phase A1 causes neural tissue todepolarize or fire. The biphasic stimulation pulse 300 shown in FIG. 3has an amplitude of 1 milliamp (mA) and a pulse width of 20 microseconds(μsec) for illustrative purposes only.

The combined areas of A1 and A2 are representative of a total amount ofelectric charge that is applied to a stimulation site by stimulationcurrent pulse 300. The biphasic stimulation pulse 300 shown in FIG. 3 is“charge balanced” because the negative area A1 is equal to the positivearea A2. A charge-balanced biphasic pulse is often employed as thestimulus to minimize electrode corrosion and charge build-up which canharm surrounding tissue. However, it will be recognized that thebiphasic stimulation pulse 300 may alternatively be charge-imbalanced asbest serves a particular application.

In some examples, the total amount of charge per phase applied to astimulation site within the cochlea by a stimulation current pulse 300corresponds to a loudness level of an input audio signal as perceived bythe patient. Hence, a change in the total amount of charge applied by astimulation current pulse 300 may result in a change in the loudnesslevel of an audio signal, which may affect the sound quality of theaudio signal as perceived by the patient.

One factor that may cause a change in the total charge per phase appliedto a stimulation site is a change in electrode impedance. FIG. 4 will beused to illustrate the relationship between charge and electrodeimpedance.

FIG. 4 shows an exemplary circuit diagram 400 representative of arelationship between current applied to an electrode 170 and theimpedance of the electrode 170. As shown in FIG. 4, the electrode 170may be connected to a voltage source 410 configured to cause a currentto be applied to the electrode 170. A return electrode 420 may also beincluded to complete the circuit. The return electrode 420 may include aground, another one of the electrode 170, and/or the housing of theimplantable cochlear stimulator 150. It will be assumed in the examplesgiven herein that the return electrode 420 is ground.

As represented by resistor 430, an impedance may be associated with theelectrode 170. The impedance may be dependent of the physiologicalproperties of the tissue where the electrode 170 is implanted, thecomposition of the electrode 170 itself, and/or any other factor as mayserve a particular application.

According to Ohm's law, the relationship between the voltage (“V”)generated by voltage source 410, the current (“I”) applied to theelectrode 170, and the impedance (“Z”) of the electrode 170 is V=I*Z.Thus, with a fixed maximum voltage, a change in impedance will cause anopposite change in the maximum current that may be applied to theelectrode 170. For example, an increase in impedance would cause adecrease in maximum current, which in turn would cause a decrease in thetotal charge per phase applied to a stimulation site. This change intotal charge applied to the stimulation site may have adverse effects onthe loudness level or sound quality of an audio signal experienced by apatient.

A change in electrode impedance may be caused by many different factors.For example, changes in one or more physiological properties of tissuewithin the cochlea, aging, a change in body fat percentage, introductionof scar tissue, dehydration, and/or infection may lead to a change inelectrode impedance. A change in electrode impedance may additionally oralternatively be caused by an electrode malfunction (e.g., an electrodemay become shorted or open). A change in electrode impedance may bepermanent in some instances (e.g., with aging) or temporary in others(e.g., during an infection).

As mentioned, a change in electrode impedance may result in adegradation of sound quality experienced by a patient. For example, achange in electrode impedance may result in a change in loudness leveland/or distort pitch.

Such sound quality degradation may adversely affect the ability of thepatient to recognize speech, music, and/or other sounds. This can beespecially devastating for pediatric cochlear implant patients becausethe change in sound quality or volume may go unnoticed for long periodsof time. Hence, an undetected change in electrode impedance canpotentially interfere with the overall speech and language developmentof pediatric patients. It will be recognized that cochlear implantpatients of all ages may experience similar difficulties if a change inelectrode impedance is not detected and accounted for. As will bediscussed in more detail below, a change in impedance may be compensatedfor by adjusting one or more of the stimulation parameters. In someexamples, the adjustment of stimulation parameters may be configured tomaintain constant a total charge per phase applied to a stimulation sitewithin the cochlea.

FIG. 5 depicts an exemplary cochlear implant system 100 configured toautomatically detect an impedance of one or more electrodes 170 inaccordance with a predefined schedule and perform one or more predefinedactions accordingly in order to maintain an optimal perceived soundquality. As shown in FIG. 5, the sound processing unit 130 may includean impedance detection module 510 configured to automatically detect animpedance of one or more of the electrodes 170 in accordance with apredefined schedule. The impedance detection module 510 may include anycombination of hardware, circuitry, and/or software configured toperform any of the functions described herein.

The impedance detection module 510 may be configured to detect one ormore electrode impedances using any suitable technique. For example, theimpedance detection module 510 may be configured to direct theimplantable cochlear stimulator 150 to apply a current pulse having aknown amplitude to each of the electrodes 170 and then measure theresulting voltages at each electrode 170. The impedance may then bedetermined by the impedance detection module 510 by dividing themeasured voltage by the known current. It will be recognized that anyother method of detecting electrode impedances may be used as may servea particular application.

As mentioned, the impedance detection module 510 may be configured toautomatically detect one or more electrode impedances according to apredefined schedule. In one particular embodiment, the impedancedetection module 510 may be configured to automatically measure theimpedances of the electrodes 170 each time the implantable coil 195 andthe external coil 190 are brought within range of one another afterhaving been separated. For example, the sound processing unit 130 isoften removed from its operating location (e.g., behind the ear) to berecharged or otherwise serviced. Additionally or alternatively, thesound processing unit 130 may be removed from its operating locationwhen the patient goes to bed or at other times as the patient maydesire. When the patient places the sound processing unit 130 back inits operating position, the impedance detection module 510 mayautomatically measure one or more electrode impedances.

Additionally or alternatively, the impedance detection module 510 may beconfigured to periodically measure one or more electrode impedances. Forexample, the impedance detection module 510 may measure one or moreelectrode impedances every twelve or twenty-four hours. It will berecognized that any time period may be used as may serve a particularapplication.

The predefined schedule may be such that the impedance detection module510 is configured to measure one or more electrode impedances inresponse to a sensed condition. For example, the implantable cochlearstimulator 150 may be configured to transmit data to the soundprocessing unit 130 representative of a status of operation of theimplantable cochlear stimulator 150. The sound processing unit 130 mayanalyze this data and determine that it is abnormal in some way. Theimpedance detection module 510 may be directed to measure one or moreelectrode impedances in response to the detected abnormality in order todetermine whether a change in impedance has caused the abnormality. Insome alternative examples, one or more electrode impedances may bemeasured whenever the user connects the sound processing unit 130 to theimplanted electrodes 170.

In some examples, the sound processing unit 130 may be configured tomaintain a log of electrode impedance measurements. In this manner, achange in one or more of the electrode impedances may be detected. Thelog may be stored as log data within one or more data storage units thatare a part of or in communication with the sound processing unit 130.

The sound processing unit 130 may be configured to perform one or morepredefined actions in accordance with the detected electrode impedances.For example, if the sound processing unit 130 determines that a changein electrode impedance has occurred, the predefined action may includealerting the patient or the patient's caregiver of the change inelectrode impedance through the use of an audible or visual alert. Inone implementation, this alert can only be sounded if the change inimpedance is deemed to cause an issue to quality of sound delivered tothe patient. For example, if it is ascertained that the implantedelectronics is not able to deliver required stimulation because ofcompliance limitations inherent in the device. In this manner, thepatient or the patient's caregiver may be put on notice that the patientmay need to visit a clinician to readjust the stimulation parametersaccordingly.

To this end, the sound processing unit 130 may include an alert facility520 configured to convey one or more alerts to the patient and/or otheruser. The alert facility 520 may include any combination of hardware,circuitry, and/or software as may serve a particular application. Forexample, the alert facility 520 may include one or more LEDs orgraphical interfaces configured to display a visual alert representativeof a detected change in electrode impedance. Additionally oralternatively, the alert facility 520 may include circuitry configuredto generate an audible beep or other sound representative of a detectedchange in electrode impedance. It will be recognized that other types ofalerts (e.g., vibrating alerts, text messages, emails, etc.) may begenerated by the alert facility 520 and communicated to the patientand/or other person as may serve a particular application.

Another predefined action that may be performed by the sound processingunit 130 in response to a detected change in electrode impedanceincludes adjusting one or more stimulation parameters to compensate forthe detected change in electrode impedance. For example, if an increasein impedance for a particular electrode 170 is detected, the soundprocessing unit 130 may be configured to adjust one or more stimulationparameters such that the total electric charge applied via the electrode170 remains constant. These changes may be made in order to attempt tomaintain a consistent loudness level as perceived by the patient.

To illustrate, a stimulation pulse applied to a particular electrode 170may be similar to that shown previously in FIG. 3. After processing thedata acquired by the impedance detection module 510, the soundprocessing unit 130 may determine that the impedance of the electrode170 has doubled. This change in impedance may result in the amplitude ofthe current applied to the electrode 170 being reduced by one half to avalue of 0.5 mA.

FIG. 6 illustrates an exemplary stimulation current pulse 600 that maybe delivered via the electrode 170 after the sound processing unit 130has adjusted at least one stimulation parameter in response to thedoubling in impedance of the electrode 170. As shown in FIG. 6, thepulse width of the stimulation current pulse 600 has been doubledcompared to the pulse width of stimulation current pulse 300 shown inFIG. 3. In this manner, the total electric charge applied via theelectrode 170 remains the same. It will be recognized that additional oralternative stimulation parameters governing the stimulation currentapplied via one or more electrodes 170 may be adjusted in response to adetected change in electrode impedance as may serve a particularapplication. Moreover, it will be recognized that the total charge perphase may be maintained constant using any other suitable method ortechnique.

Additional or alternative stimulation parameters may be adjusted tocompensate for a detected change in electrode impedance. For example, amost comfortable stimulation level (“M level”) and/or a quiet soundlevel (“T level”) corresponding to electrical stimulation applied to apatient may be adjusted to compensate for a detected change in electrodeimpedance. Additionally or alternatively, values corresponding to acurrent amplitude versus pulse width curve may be stored in a look uptable and used to determine an appropriate pulse width for a particularcurrent amplitude caused by a change in impedance. These values may beobtained using any suitable heuristic and/or empirical data as may servea particular application.

As mentioned, an electrode 170 that malfunctions or otherwise becomesdisabled may result in a change in impedance of the electrode 170 and/oran abnormal impedance measurement. For example, an electrode 170 maybecome shorted or open. A shorted electrode 170 may have an impedancesubstantially equal to zero ohms. An open electrode 170 may have arelatively very large impedance value. Other electrode malfunctions mayinclude, but are not limited to, partial shorting, irregular stimulationperformance, etc. Such disabled electrodes may result in decreased soundquality and/or distorted pitch and may even render a cochlear implantsystem 100 useless to a patient.

In some examples, when the impedance detection module 510 detects anelectrode impedance value indicative of a disabled electrode, the soundprocessing unit 130 may be configured to use current steering and/orother techniques to compensate for the disabled electrode.

Current steering may be used in configurations wherein a desiredstimulation site corresponding to a disabled electrode 170 is locatedspatially in between two functioning electrodes 170. To effectivelydeliver stimulation to the stimulation site previously stimulated by thedisabled electrode 170, weighted current may be applied simultaneouslyor in a time-interleaved manner via two or more electrodes 170surrounding the disabled electrode 170. The basis for current steeringis the phenomenon of summation of electrical fields, where the currentdelivered to the two electrodes sums together. A stimulation sitelocated spatially in between the two electrodes 170 may be effectivelystimulated due to the summation of electrical fields.

Current steering will be further explained with reference to FIG. 7.FIG. 7 is a functional block diagram of an exemplary current steeringstrategy as applied via the cochlear implant system 100 of FIG. 5. Thecurrent steering strategy is configured to dynamically focus one or moreexcitation fields produced by current steering electrodes. It will berecognized that the strategy shown in FIG. 7 is merely exemplary andthat it may include additional or alternative components and/orfunctions.

As shown in FIG. 7, a disabled electrode 170-1 may be surrounded by aplurality of properly functioning electrodes 170-2 through 170-5. All ofthe electrodes shown in FIG. 7 will be referred to herein collectivelyas “electrodes 170”.

An input audio signal is filtered by one or more filters 700 configuredto divide the signal into a number of frequency channels or bands. Theinput audio signal is also input into a frequency estimator 710configured to estimate the peak frequency thereof. A time pattern block720 is configured to build construct the temporal structure of a pulsetrain representing the signal output by the filter 700.

Mapping stages 730 are configured to map the amplitude of the signaloutput by the time pattern block 720 to corresponding current levels inaccordance with a suitable mapping function.

The output of each mapping stage 730 is input into a current steeringblock 740. The current steering block 740 is also configured to receivethe output of the frequency estimator 710. In some examples, the currentsteering block 740 is configured to determine appropriate weightingfactors for current to be applied via at least two electrodes thatsurround the disabled electrode 170-1 (e.g., electrodes 170-2 and170-3). This determination may be based at least in part on the peakfrequency estimate and the output of each of the mapping functions 730.The weighting factors may be applied to the current using multiplicationblocks 750. In this manner, stimulation current may be delivered to astimulation site located in between the functioning electrodes 170-2 and170-3.

The excitation field produced by electrodes 170-2 and 170-3 may benarrowed by applying compensating current simultaneously or in atime-interleaved manner via one or more additional electrodes (e.g.,electrodes 170-4 and/or 170-5). A focusing factor generator 760 may beincluded and configured to generate the aforementioned focusing factor abased on the amplitude of the signal output by the filter 700. Thefocusing factor a is used to generate scaled versions of the currentsteering current. This scaled current is delivered via the one or moreadditional electrodes 170-4 and 170-5 to effectively narrow theexcitation field produced by electrodes 170-2 and 170-3.

As shown in FIG. 7, loudness compensators 770 may also be included. Theloudness compensators 770 are configured to adjust the amplitudes of thecurrents applied via electrodes 170-2 and 170-3 to compensate forloudness changes that may be caused by current delivered via thecompensating electrodes 170-4 and 170-5.

FIG. 8 illustrates an exemplary method of automatically detecting animpedance of one or more electrodes in a cochlear implant system. WhileFIG. 8 illustrates exemplary steps according to one embodiment, otherembodiments may omit, add to, reorder, and/or modify any of the stepsshown in FIG. 8.

In step 810, an implantable cochlear stimulator coupled to one or moreelectrodes is provided. The implantable cochlear stimulator may besimilar to implantable cochlear stimulator 150, for example.

In step 820, an electrical stimulation current is generated with theimplantable cochlear stimulator in accordance with one or morestimulation parameters. The stimulation current may be generated in anyof the ways described herein.

In step 830, an impedance of at least one of the electrodes isautomatically detected in accordance with a predefined schedule. Theimpedance of at least one of the electrodes may be detected in any ofthe ways described herein.

In step 840, a predefined action is performed in accordance with thedetected impedance. The predefined action may include, but is notlimited to, alerting the patient, a clinician, and/or other user,adjusting one or more stimulation parameters to compensate for a changein impedance, and/or maintaining constant a total electric chargeapplied via one or more electrodes as may serve a particularapplication.

The preceding description has been presented only to illustrate anddescribe embodiments of the invention. It is not intended to beexhaustive or to limit the invention to any precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching.

1. A method comprising: directing, by a sound processing unit, animplantable cochlear stimulator coupled to a plurality of electrodes togenerate an electrical stimulation current in accordance with one ormore stimulation parameters; automatically detecting, by the soundprocessing unit, an impedance of at least one of the electrodes; anddirecting, by the sound processing unit in accordance with the detectedimpedance, the implantable cochlear stimulator to adjust a pulse widthof the electrical stimulation current to maintain constant a totalelectric charge level of the electrical stimulation current.
 2. Themethod of claim 1, wherein the directing of the implantable cochlearstimulator to adjust the pulse width of the electrical stimulationcurrent comprises adjusting at least one of the one or more stimulationparameters.
 3. The method of claim 1, wherein the automaticallydetecting comprises detecting the impedance in accordance with apredefined schedule.
 4. The method of claim 3, wherein the predefinedschedule comprises a periodic schedule.
 5. The method of claim 1,wherein the automatically detecting comprises detecting the impedanceeach time the implantable cochlear stimulator is connected to the soundprocessing unit.
 6. The method of claim 1, further comprising directing,by the sound processing unit in accordance with the detected impedance,the implantable cochlear stimulator to adjust at least one of a mostcomfortable current level and a quiet sound level.
 7. The method ofclaim 1, further comprising providing, by the sound processing unit, analert if the detected impedance represents a change in impedance.
 8. Themethod of claim 1, further comprising directing, by the sound processingunit in accordance with the detected impedance, the implantable cochlearstimulator to maintain a consistent loudness level of an audio signal asperceived by a patient associated with sound processing unit.
 9. Themethod of claim 1, further comprising directing, by the sound processingunit in accordance with the detected impedance, the implantable cochlearstimulator to maintain a consistent sound quality of an audio signal asperceived by a patient associated with sound processing unit.
 10. Amethod comprising: directing, by a sound processing unit, an implantablecochlear stimulator coupled to a plurality of electrodes to generate anelectrical stimulation current in accordance with one or morestimulation parameters; automatically detecting, by the sound processingunit, an impedance of at least one of the electrodes; using, by thesound processing unit, the detected impedance to identify a disabledelectrode included in the plurality of electrodes; and directing, by thesound processor, the implantable cochlear stimulator to use currentsteering to compensate for the disabled electrode.
 11. The method ofclaim 10, wherein the automatically detecting comprises detecting theimpedance in accordance with a predefined schedule.
 12. The method ofclaim 11, wherein the predefined schedule comprises a periodic schedule.13. The method of claim 10, wherein the automatically detectingcomprises detecting the impedance each time the implantable cochlearstimulator is connected to the sound processing unit.
 14. A systemcomprising: a processor configured to direct an implantable cochlearstimulator coupled to a plurality of electrodes to apply an electricalstimulation current by way of at least one electrode included in theplurality of electrodes in accordance with one or more stimulationparameters; and an impedance detection module configured toautomatically detect an impedance of the at least one electrode; whereinthe processor is further configured to adjust, in accordance with thedetected impedance, a pulse width of the electrical stimulation currentto maintain constant a total electric charge level of the electricalstimulation current.
 15. The system of claim 14, wherein the processoris configured to adjust the pulse width of the electrical stimulationcurrent by adjusting at least one of the one or more stimulationparameters.
 16. The system of claim 14, wherein the impedance detectionmodule is configured to automatically detect the impedance by detectingthe impedance in accordance with a predefined schedule.
 17. The systemof claim 16, wherein the predefined schedule comprises a periodicschedule.
 18. The system of claim 14, wherein the impedance detectionmodule is configured to automatically detect the impedance by detectingthe impedance each time the implantable cochlear stimulator is connectedto the sound processing unit.
 19. The system of claim 14, wherein theprocessor is further configured to provide an alert if the detectedimpedance represents a change in impedance.
 20. The system of claim 14,wherein the processor is further configured to direct the implantablecochlear stimulator to maintain a consistent loudness level of an audiosignal as perceived by a patient.